I'm the type of guy that believes that understanding something makes us feel better about it. So, I would organise a group of students that would undertake the task of creating a video documentary about the life of the departed student (with interviews of his fellow students and his teachers) and another that would make a research about depression (reading books and consulting experts on the field). Those works would remain in the school library, in memory of the student that took his life. Maybe this would help other students with similar problems understand depression and avoid getting in the same situation.

You could also organise a group that would create a sculpture or painting in memory of the student, to place in a specific spot in or about the school.

Mural painting would be an idea if there's a feeling of a need from the entire community. Let the kids figure out what to draw and paint on the wall. Through the process, by discussing the topic, you could teach them a lot of things, and the finished art would be a good tribute.

I think the point is to have as many people involved in the making of art.